The present invention relates to the cooling of electronic components which generate high amounts of heat in general and more particularly to a method and apparatus for removing heat from an electronic heat generating component in an electronic system having a small form factor.
A number of present day electronic components utilized, for example, in computer systems, generate large amounts of heat. These components, such as microprocessors and associated components are typically encapsulated in plastic or ceramic from which a plurality of leads extend. The integrated circuit (IC) is mounted to a printed circuit board either by direct soldering or through a connector which is soldered to the printed circuit board. In a typical personal computer system, a processor, which in most cases in current systems is a high speed processor which generates a great deal of heat, is mounted on a printed circuit board known as a motherboard, along with a plurality of other components that support the processor such as memory circuits. Also contained within the personal computer housing are additional circuits or circuit boards such as video cards, facsimile-modem cards, etc. The housing may also contain a power supply, supplying power to all of the various components.
As explained in co-pending application Ser. No. 08/686,856, filed May 31, 1996 and assigned to the same assignee as the present invention, the disclosure of which is hereby incorporated by reference in its entirety, it is desirable to have a high rate of heat transfer from the IC package in order to maintain junction temperatures within the IC inside safe operating limits. As noted, modern microprocessors typically employ millions of transistors in internal circuitry that requires some type of cooling mechanism to avoid excessive junction temperatures that may effect the performance of the circuit and can cause permanent degradation of the device. As noted in that application, this is a particularly difficult problem in the design of computer system enclosures which have a small form factor such as laptop and notebook computers. However, heat removal also can constitute a problem in other types of systems which have high power profile components located within a small form factor or thin profile electronic device.
Aside from the possibility of affecting the performance of the circuits in the IC and degradation of those circuits, high heat generating components which are located within consumer electronic devices, such as laptop computers, can create hot spots at certain locations along the external casing of the devices. These hot spots can be uncomfortable to touch and may even cause burns. This is a farther reason for conducting heat away from these hot spots and cooling the components generating them to avoid injury to users.
The aforementioned application describes prior art methods used to remove heat from heat generating components located within the confines of a computer enclosure, which include the simple attachment of finned-heat sinks; the development of finned-heat sinks with intricate fins; the use of large flat heat spreading plates to which an IC is directly or indirectly attached; and the thermal coupling of the integrated circuit to a heat spreading plate by a heat pipe or other low resistance thermal path. As described, more recently, forced cooling air has been used to cool one side of a heat spreading plate having an integrated circuit attached to the other side. The prior application recognizes that these prior art methods do not provide sufficient heat removal capacity and/or efficiency needed to cool current and future high performance microprocessors and other high heat generating devices in portable general purpose or other thin profile electronic devices.
The solution proposed in that application is the use of an air duct comprising a thermally conductive housing having internal fins dispersed along the internal walls of the air duct. An airflow generator, e.g., a fan, produces an airflow that is directed from an inlet port located at or near the center of the air duct to first and second exit ports located adjacent opposite ends of the duct. The heat generating integrated circuit such as a microprocessor is thermally coupled to the thermally conductive housing by means of a low resistance thermal path such as a heat pipe.
Such an arrangement efficiently removes large amounts of heat. However, the location of the inlet port near the center of the air duct as described in the aforementioned application requires openings above the air inlet in the housing of the device. In the case of a laptop computer this can cause a problem, since in many current laptop computers, a convenient place to locate such openings is not available because it would occur in the area of the keyboard.
Because of this, there is a need for an improved apparatus and method to solve the problem of cooling high heat generating components such as microprocessors within portable consumer electronic and computer devices, which retain the highly efficient cooling performance of the aforementioned application within the available space, but avoid the problem of drawing air in through the top surface of the device in order that it can be used with a device such as a laptop computer which does not have an area on its top surface available for air intake.
The present invention provides such an apparatus for cooling a heat generating component through the use of an elongated hollow heat exchanger with a fan at one end of the heat exchanger. A heat pipe has one end thermally coupled to the heat exchanger and the other end adapted to be thermally coupled to the heat generating component. When used in a small form factor, low profile electronic device such as a laptop computer, the heat generating component, e.g., a microprocessor, is coupled to the heat pipe. In the illustrated embodiment, a heat sink is thermally coupled to the heat pipe, the heat sink being in thermal contact with the heat generating component.
Various embodiments of the present invention are disclosed including one in which one end of the heat pipe is in thermal contact with the outside surface of the heat exchanger duct. Preferably there are members, e.g., fins, attached to the inner surface of the heat exchanger duct increasing its internal surface area. The heat exchanger duct may have a rectangular or cylindrical cross section.
The members on the inside may take various forms such as convoluted fins, plate fins or pin fins. In another embodiment, the heat pipe extends through the center of the hollow heat exchanger duct and a plurality of longitudinal radial fins extend between the heat pipe and the inside wall of the heat exchanger duct, supporting the heat pipe. In the illustrated embodiment, the fan draws air through the heat exchanger duct. It could equally well blow air into the heat 20 exchanger duct.
In the illustrated laptop application, the heat exchanger extends in a direction adjacent and parallel to one of the side walls of the laptop housing. An air outlet is formed in the rear wall and an air inlet in the side wall to which the heat exchanger is adjacent. The fan is disposed between the air outlet and the one end of the heat exchanger. In some embodiments there is a curved deflector between the inlet opening and the other end of the heat exchanger and/or an expansion duct between the one end of the heat exchanger and the fan.
The arrangement of the present invention allows the use of the vertical walls as an air inlet and outlet, thus avoiding interference with elements such as a keyboard on the top of the device. This is done by thermally coupling one end of a heat pipe having two ends, to the heat generating component, such as a microprocessor, thermally coupling the other end of the heat pipe to an elongated hollow heat exchanger and generating a flow of air through the hollow heat exchanger using a fan disposed at one end while drawing air in through the other end.